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A spreadsheet for calculating normative mole fractions of end-member species for Na-Ca-Li-Fe2+-Mg-Al tourmalines from electron microprobe data

  • George B. Morgan EMAIL logo
Published/Copyright: January 9, 2016
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American Mineralogist
From the journal American Mineralogist Volume 101 Issue 1

Abstract

This work presents a spreadsheet that calculates the mole fractions of end-member components for simple Na-Ca-Li-Mg-Fe2+-Al tourmalines from electron microprobe data. The input includes the B2O3 concentration obtained either from direct analysis or by estimation on the basis of stoichiometry. The concentration of Li2O can either be input from other analysis or estimated by the spreadsheet. The spreadsheet does not address the mole fractions of Cr, V, oxidized or deprotonated tourmaline species, nor account for species involving tetrahedral boron or aluminum. Therefore, the spreadsheet is not a comprehensive tool that includes all IMA approved tourmaline species, and so is not intended for naming tourmalines according to IMA convention. The present method includes a useful subset of end-member species that can be described simply from electron microprobe data and so, akin to a normative mineralogical analysis for rock composition, the calculations are intended to provide a normative result that serves as simple basis for comparing tourmalines that is more direct than names derived from the most abundant species present.

Keywords: Tourmaline; formula; mole fractions; end-members; electron microprobe analysis

Acknowledgments

The author thanks Christine Clark, Peter Bačík, and Milan Novak, whose thoughtful reviews of the first submission of this work spurred a necessary reassessment of the calculational model and, therefore, significantly improved all aspects of the manuscript. In this regard, special thanks are given to Peter Bačík who tested the previous model with natural compositions from his own database, some of which have been incorporated in this work as computational test cases. The re-submitted manuscript was further strengthened by reviews of Peter Bačík and Ferdinando Bosi. The Electron Microprobe Laboratory gratefully acknowledges generous supported by the Office of the Vice President for Research at the University of Oklahoma.

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  1. Manuscript handled by G. Diego Gatta.

Received: 2015-4-29
Accepted: 2015-7-22
Published Online: 2016-1-9
Published in Print: 2016-1-1

© 2016 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2016-5392
Keywords for this article
Tourmaline; formula; mole fractions; end-members; electron microprobe analysis

Articles in the same Issue

  1. Highlights and Breakthroughs
  2. A spin on lower mantle mineralogy
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